In rotary internal combustion engines having fuel combustion systems comprising an unthrottled air intake port and controlled injection of fuel, known as stratified charge fuel systems and as exemplified in the U.S. Pat. No. 3,246,636 to Bentele, dated Apr. 19, 1966; Jones, U.S. Pat. No. 3,393,667, dated July 23, 1968; and Jones, U.S. Pat. No. 3,698,364, dated Oct. 17, 1972, fuel injection is usually provided for by jerk pumps of the positive displacement plunger type. In this type of fuel injection pump such as is disclosed in the U.S. Pat. No. 2,565,681 to Fleck et al, dated Aug. 28, 1951, fuel is discharged to the combustion chambers of the engine by a cam actuated, reciprocable plunger, the rotational speed of the cam being proportional to the rotor speed of the engine for proper timing of the injections of fuel. The injection pump also includes a means for changing the effective stroke of the plunger in accordance with engine load or demand so that controlled amounts of fuel are injected into the combustion chambers at proper times.
In such engines having stratified charge fuel systems, above described, it has been found that, in spite of the fact that the angular speed of the pump cam is directly proportional to rotor rotation, the duration of fuel injection, relative to the angular rotor displacement (crank angle) for any given quantity of fuel, varies to a greater extent than is attributable to change in the speed of rotor rotation. More specifically, the efficient combustion of fuel is adversely affected when the engine speed changes from the speed at which the cam profile and fuel injection nozzles have been selected for optimum performance. This condition is attributable to the increased fuel injection duration relative to rotor velocity at high engine speeds due to expansion of the fuel feed conduits between the pump discharge and the fuel injection nozzles when, at high engine speeds, the pump plunger is actuated at high linear velocities. Expressed in another way, fuel injection duration is increased by reason of continued fuel injection after full discharge stroke of the pump plunger due to contraction of the fuel feed conduits following their expansion due to a substantial increase in fuel discharge pressure at high pump plunger linear velocities. It should be pointed out that these pressures are very substantial and can reach pressure values as high as 40,000 psi. This phenomenon results in the injection of fuel into the combustion chambers for different periods of time relative to crank angle or angular sweep of the rotor at high and low engine (rotor) speeds which causes changes in the air-fuel ratio in localized areas of the combustion chamber and hence the efficiency of fuel combustion and engine performance.
It is therefore an object of this invention to provide, in a rotary internal combustion engine, an improved fuel injection system having a positive displacement fuel pump, which system achieves improved fuel combustion over a wide range of engine speeds.
It is another object of the present invention to provide in a rotary internal combustion engine an improved fuel injection system having a positive displacement fuel pump wherein the duration of fuel injection at any given load is for the same amount of angular rotor displacement at both high and low rotor speeds.